Re: A weighty subject

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

On Fri, 15 Oct 1999, Richard Tarara wrote:

> It seems to me that the problem with Leigh's and John's definition of weight
> is a conceptual one for intro students.  In most force based problems, one
> of the forces is often labeled WEIGHT (OK, you _could_ label it the
> Gravitational Force of the Earth on the object..but that is awkward and you
> have tens of thousands of instances of the other to expunge). ...

Fine.  Then that's the end of the story as far as I am concerned.  In
introductory physics we *do* need to have a name for things like like
GMm/R^2. If you are unwilling to call it "the force of gravity" then
"weight" is probably the next best thing.  And if you have decided to use
the term "weight" in this manner, then it is no longer available for use
in any other manner.

(I would point out, however, that many texts use the term "weight" to
describe *both* things.  They usually start out defining weight as m*g
where g is the so-called "acceleration due to gravity" as determined by
dropping something.  This happens, in fact, to agree with my definition.
Later, however, after introducing the gravitational force, some define
weight as the magnitude of the force that results from the use of Newton's
law of universal gravitation--your definition.  Then some proceed to
thoroughly confuse matters by talking about the centrifugal correction in
an attempt to reconcile these two utterly irreconcilable definitions!)

All I am really saying is that I think it is terribly unfortunate to waste
two perfectly good terms on describing the *same* thing especially when
even the common meanings seem so different in many circumstances--e.g.,
weightless astronauts.

So IMO you've made an unfortunate decision, but you are certainly not
"wrong"!

John Mallinckrodt      mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm